Field of the Invention
The invention relates in general to a decision feedback equalizer, and more particularly, to a decision feedback equalizer capable of enhancing the computation performance and a control method thereof.
Description of the Related Art
FIG. 1 shows a functional block of a conventional decision feedback equalizer (DFE). A transmitted signal x(n) passes through a channel 10 and is affected by noise r(n) to become an input signal y(n) of a DFE 100, where n represents a time index. The DFE 100 includes a feed-forward equalizer (FFE) 110, a decider 120, a feed-backward equalizer (FBE) 130, a channel estimator 140, an FFE coefficient calculating unit 150, and an FBE coefficient calculating unit 160. One main function of the FFE 110 is processing pre-cursor inter-symbol interference signals and a part of post-cursor inter-symbol interference signals in the input signal y(n). One main function of the FBE 130 is processing post-cursor inter-symbol interference signals in the input signal y(n). The decider 120 then generates a decision signal x′(n) according to filtering results of the FFE 110 and the FBE 130.
An FFE coefficient the FFE 110 needs for operations and an FBE coefficient b the FBE 130 needs for operations are respectively generated by the FFE coefficient calculating unit 150 and the FBE coefficient calculating unit 160. The FFE coefficient calculating unit 150 generates the FFE coefficient f according to a channel impulse response (CIR) estimation vector h generated from the input signal y(n). The FBE coefficient calculating unit 160 generates the FBE coefficient b according to the CIR estimation vector h and the FFE coefficient f.
A minimum mean square error (MMSE) equalizer is a common type of a decision feedback equalizer (DFE), and features an advantage of leaving noise r(n) unamplified. Fast transversal recursive least squares (FT-RLS) are one most common algorithm for calculating the FFE coefficient f and the FBE coefficient b, and feature an advantage of having a fast convergence speed. An optimum FFE coefficient f and an optimum FBE coefficient b of an MMSE-DFE may be represented as follows:f=((Φhh−HHH)+φn2I)−1h  (1)b=HH×f  (2)
In the above equations, the CIR estimation vector h=[h(Δ)h(Δ−1) . . . h(Δ−LF+1)], where Δ represents a decision delay, LF is the length of the FFE 110, the FFE 110 is an (LF−1)-order equalizer and LF is a positive integer, Φhh represents a channel autocorrelation matrix, σn2 represents noise energy, I represents a unit matrix, and the CIR estimation matrix h may be represented as:
                    H        =                  [                                                                      h                  ⁡                                      (                                          Δ                      +                      1                                        )                                                                              …                                                              h                  ⁡                                      (                                          Δ                      +                                              L                        B                                            -                      1                                        )                                                                                                                        h                  ⁡                                      (                    Δ                    )                                                                              …                                                              h                  ⁡                                      (                                          Δ                      +                                              L                        B                                            -                      2                                        )                                                                                                      ⋮                                            ⋱                                            ⋮                                                                                      h                  ⁡                                      (                                          Δ                      -                                              L                        F                                            +                      2                                        )                                                                              …                                                              h                  ⁡                                      (                                          Δ                      +                                              L                        B                                            -                                              L                        F                                                              )                                                                                ]                                    (        3        )            
Wherein, LB is the length of the FBE 130, the FBE 130 is an (LB−1)-order equalizer, and LB is similarly a positive integer.
It is known from equations (1) and (2) that, the computation complexity of the FFE coefficient f is far greater than that of the FBE coefficient b. Therefore, it is an important task of the technical field to provide a more efficient computation method for enhancing the performance of the DFE.